1. For any given day, the number of degrees that the average temperature is below 18°C is called the degree-days for that day. This figure is used to calculate how much is spent on heating. The total
number D of degree-days for each month in Dubuque, Iowa, with t = 1 representing January, can be
modelled using the function D(t) = 704 sin 30(t - 2) + 716 .

a) What month has the lowest total number of degree-days over the whole year?

b) What is minimum total number of degree-days?

c) What is the total number of degree-days on September 30?

d) When is the total number of degree-days at 1068? How many months is it below 1068 degree-days?